Plastic bag for the vacuum preservation of food

ABSTRACT

A bag of plastic material for vacuum preservation of food comprises two rectangular walls joined together along three sides. The width of one of the walls is larger than the width of the other wall by a predetermined quantity, preferably about 5%.

BACKGROUND OF THE INVENTION

[0001] This invention is concerned with a bag of plastic material for the vacuum preservation of foodstuffs in home.

[0002] It is a widespread practice nowadays to pack vegetables, meat, cheese and other foodstuffs in bags or envelopes for protection and preservation, the bags being then stocked in refrigerators. The bags comprise two walls of a plastic material, welded together along three sides. The walls are usually many-layered polyethylene sheets, which are compatible with food but are impermeable to gas. In order to improve preservation of certain quick-spoiling foodstuffs, it has recently become more usual to evacuate the bag. Air is evacuated from the bag by means of a vacuum pump or by other means, and the bag is then tightly sealed at its mouth by hot-welding.

[0003] However, the internal bag surfaces in conventional bags are liable to adhere locally to each other or to any smooth, wet surface of the food, thereby giving rise to self-contained air pockets which are not emptied during air extraction and therefore remain in the sealed bag. In order to prevent the formation of such air pockets, it has been proposed to provide one of the bag walls with embossed blobs or projections or crests, in order to provide a network of furrows or channels which will afford the air a path to the bag mouth, where suction takes place.

[0004] EP-A 1 281 625 discloses a different device for preventing the formation of air pockets, whereby the inside of one of the bag walls is hot-printed with two or three rectilinear rough bands, extending longitudinally over the entire length of the bag. The bands are produced by applying a welding bar lined with teflon against the sheet comprising the bag wall.

SUMMARY OF THE INVENTION

[0005] It is now the main object of the invention to provide a bag of plastic material for vacuum preservation of foodstuffs, which avoids the drawback of the trapped air pockets, and which, at the same time, is cheaper to manufacture than bags with embossed or rough walls, and which allows the bag to be manufactured cheaply on conventional assembly lines, without a need for additional complex machinery.

[0006] The above and other objects and advantages, such as will appear from the following disclosure, are achieved by the invention with a bag of plastic material having the features recited in claim 1, the dependent claims reciting other advantageous features.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] A preferred embodiment of the invention will now be described, by way of non-limiting example, with reference to the attached drawings, wherein:

[0008]FIG. 1 is a perspective view of a bag according to the invention;

[0009]FIG. 2 is a front view of the inventive bag during air extraction;

[0010]FIG. 3 is a diagrammatical side view of equipment for mass manufacturing bags according to the invention;

[0011]FIG. 4 is a diagrammatical front view of an alternative technique for mass manufacturing bags according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0012] With reference to the Figures of the drawings, a bag 10 comprises two rectangular walls 12 and 14, which are joined together along their edges on three sides 30, 32, 34 by welding. Each wall, as known per se, is made of a many-layered plastic material, comprising an inner polyamide layer, which imparts a good mechanical resistance to the bag and also is an effective barrier to the leaking of air, and sandwiched between two outer layers of polyethylene, a material that is food-compatible and is easily weldable.

[0013] According to the invention, the width of wall 12 across the side welds 30, 34 exceeds the width L of wall 14 by a quantity in the range 2% to 10%, preferably 5%. Consequently, wall 12 is slack with respect to wall 14 in the transverse direction, so that it will show undulations when wall 14 is distended.

[0014] As shown on FIG. 2, during the evacuation of air, when the opposite walls are squeezed between the lips of the extractor near the mouth of the bag (not shown), passages are created, such as 18, in a substantially longitudinal direction and with random distribution, the passages providing exit paths for the air.

[0015] The slack wall of the bag will of course be crumpled into small folds at the transverse weld 32 along the bottom of the bag, and in order to insure that a dependable, air-tight weld is obtained, the weld will preferably be made wider than the longitudinal welds 30, 34. This will improve the sealing at spots where leak passages might develop along the joining line between the flat surface of wall 14 and the wavy surface of wall 12.

[0016] A known system for manufacturing conventional bags comprises, as shown on FIG. 3, two reels 20, 22, from which respective ribbons 24, 26 are unrolled to form the walls of the bag. Transverse welds 28 are made at predetermined intervals along the ribbons by means of welding bars B1, B2, in order to define the side borders of the bag, and longitudinal welds are also made on one of the edges of the ribbon to define the bottom of the bag. In order to have one slack wall, ribbon 24 is pulled at a speed V1 slightly in excess of the speed V2 of ribbon 26, so that excess material is fed forward between successive welds.

[0017] According to an alternative technique for the manufacture of bags, the sides of the bag are defined by longitudinal welds 130, 132, made along the edges 124, 126 of the ribbons as they unroll from the reels (not shown), and the bottom of the bag is made by transverse, spaced welds. In this case, as shown on FIG. 4, the slackness in one of the walls is obtained by interposing a humped plate 134 between the ribbons.

[0018] The bag according to the invention can be manufactured by making only minor modifications to conventional bag manufacturing equipment.

[0019] As a further advantage of the invention, the bag has the same degree of pliability of a conventional bag, so that it can easily match the changing shapes of the contents.

[0020] A preferred embodiment of the invention has been described, but modifications can of course be made to it by a person skilled in the art within the scope of the same inventive concept. By way of example, both walls might be integral with each other along one of the longitudinal edges, with welds made only on the other side and along the bottom.

[0021] The disclosures in Italian Utility Model Application No. TO2003U000089 from which this application claims priority are incorporated herein by reference. 

What is claimed is:
 1. A bag of plastic material for the vacuum preservation of foodstuffs, comprising two rectangular walls joined together along three sides, wherein the width of one of the walls is larger than the width of the other wall by a predetermined quantity.
 2. The bag of claim 1, wherein the quantity by which the width of one wall exceeds the width of the other wall is in the range 2% to 10%.
 3. The bag of claim 2, wherein said excess quantity is 5% of the width of said other wall.
 4. A process for mass-producing bags according claim 1, wherein two superposed ribbons of plastic sheet are continuously fed along a path and transverse welding bars are applied at intervals to the ribbons to obtain welds joining the ribbons together to form longitudinal sides of the bag, characterized in that one of the ribbons is fed at a higher speed than the other ribbon.
 5. A process for mass-producing bags according claim 1, wherein two superposed ribbons of plastic sheets are continuously fed along a path and longitudinal welding bars are applied to the opposite edges of the ribbons to obtain welds joining the ribbons together to form longitudinal sides of the bag, wherein a humped plate is inserted between the ribbons. 